1. Field of the Invention
The present invention relates to a recording and/or reproducing apparatus for recording informational signals on a magneto-optical disc and/or reproducing the recorded informational signals from the magneto-optical disc.
2. Prior Art
Optical disc which are capable of writing and reading informational signals and used as recording media for informational signals have heretofore been proposed.
Such a magneto-optical disc has a recording layer a of a magnetic thin film which can be perpendicularly magnetized. To record information, the signal recording layer is heated to a temperature higher than the Curie temperature by irradiation with a laser beam and the direction of magnetization is reversed by the application of an external magnetic field. To read recorded information, the signal recording layer is irradiated with a linearly polarized flux of lights such as a laser beam to detect the change in the direction of polarization due to Kerr's effect which occurs on deflection of the flux of lights on the surface of the signal recording layer so that differences in the direction of magnetization are read.
In order to perform writing and/or reading of the informational signals on and/or from such a magneto-optical disc, a magneto-optical disc recording and/or reproducing apparatus comprising an optical pickup device and a magnetic head device including a magnetic head for applying an external magnetic field are used.
The optical pickup device is formed so that it irradiates one main side of the magneto-optical disc with a converged laser beam and detects the reflected light of the laser beam from the magneto-optical disc.
On the other hand, the magnetic head device is formed so that it applies a magnetic field on the magneto-optical disc from one side thereof which is opposite to the side irradiated with the laser beam.
Writing and/or reading of the informational signals on and/or from the surface of the magneto-optical disc is achieved by rotating the magneto-optical disc and by moving an optical pickup device and the magnetic head along the magneto-optical disc in a radial direction of the disc in synchronization with each other.
The magneto-optical recording and/or reproducing apparatus which uses a magneto-optical disc as a recording medium is formed so that a recording or erasing operation of information signals is achieved with a thermal energy of a laser beam impinged upon the magneto-optical disc from the optical pickup device and a bias magnetic field applied upon the magneto-optical disc from the magnetic head which is an external magnetic field generator.
In the magneto-optical recording and/or reproducing apparatus which performs the foregoing operation, the external magnetic field generating device for applying the external magnetic field upon the magneto-optical disc is not used except in the case in which recording and erasing of the informational signals on and from the disc is performed. Therefore, it is preferable that the external magnetic field generating device be positioned outside of the locus of loading the disc on the disc cartridge during the loading and unloading operation of the magneto-optical disc. A similar placement is desirable when loading and unloading the disc cartridge upon and from the recording and/or reproducing apparatus which requires that the external magnetic field generating device be moved to a given position, that is, a position close to the magneto-optical disc in association with completion of the loading operation.
An option may be considered that the foregoing moving operation of the external magnetic field generating device is realized by a switch which is turned on and off in response to the lifting operation of the cartridge holder for holding the disc cartridge to load the same and a moving mechanism which is initiated to start the driving by the switch.
However, if a mechanism for moving the external magnetic field generating device, drive of which is a initiated by a switch which is turned on or off in association with the the lifting operation of the cartridge holder is separately provided to control the movement of the external magnetic field generating device, the moving mechanism becomes more complicated, and ultimately results in a more complicated recording and/or reproducing apparatus.